1. Field of Invention
The invention relates to a sound fast-forward playing method and device, and, in particular, to a sound fast-forward playing method and device, which is used for an audio decoding system.
2. Related Art
The fast-forward playing, such as double speed or high speed fast-forward playing, is a convenient function for a user to search the desired music section or content. If the multi-channel (AC3, DTS, MPEG MultiCH, MLP) or two-channel (CDDA, MP3, MPEG) audio decoding system plays a fast-forward, the following four methods may be concerned. The first method is to increase sampling frequency so as to decode all data and to play it. In this case, the digital/analog converter (DAC) should be adjusted higher, which results in the key increase and generates grating sound. The second method is to increase sampling frequency so as to decode all data and then to lower the key with down sampling technology, so that the user would not hear the voice with risen key. The third method is to play skipped data, so it is unnecessary to adjust the DAC. The fourth method is to play a mute mode.
In the previously mentioned first and second methods, since the processor, such as CPU or DSP, has limitation on calculating speed, it may fail to exactly match the sound sampling frequency increased for the continuously fast-forward play. Furthermore, the performance of the hardware may be greatly decreased. In the two-channel or multi-channel audio decoding system, the performance of hardware is a very important resource. For example, the performance of hardware is 50 MIPS for DTS 5.1 surround decoding, and is more than 65 MIPS for MLP decoding. In double speed or high speed fast-forward playing, the required value of MIPS is doubled. If the calculating speed of processor cannot match the sound sampling frequency increased for the continuously fast-forward play, the conventional DVD player may play mute mode or play skipped data. However, when the DVD player plays skipped data for fast-forward playing, since some sound data are skipped, the broken noise due to the discontinuous point of sound wave may occur. This will affect the user while determining the content of the played sound, and, also, the broken noise is grating.
It is therefore an important objective of the invention to provide a sound fast-forward method without occupying much hardware performance and to make the sound wave more continuous for preventing broken noise.